1. Field of the Invention
The present invention relates generally to a method of forming patterns, and more particularly to directed self-assembly (DSA) pattern formation in the semiconductor fabricating process.
2. Description of the Prior Art
As dimensions of semiconductor devices continue to shrink, the demand for the resolution of a photolithographic process goes up correspondingly. Typically, photolithography involves passing light through a reticle and focusing the light onto a photochemically-active photoresist material. By directing light or radiation through the reticle, the pattern in the reticle may be focused on the photoresist. The light or radiation causes a chemical change in the illuminated parts of the photoresist, which allows those parts to be selectively retained or removed, depending upon whether positive or negative photoresist is used, relative to parts which were in the shadows. Thus, the exposed and unexposed parts form a pattern in the photoresist.
Because the resolution of a photolithographic process is dependent upon wavelength of a light source used in the photo-exposure, the mask patterns obtained by conducting a photolithographic process must be separated from each other by a minimum distance. After being developed, the photoresist acts as a mask to transfer a pattern to an underlying material. The photoresist is sufficiently robust to withstand the development step without deforming and is also sufficiently robust to withstand an etching process for transferring the mask pattern to an underlying material. However, the photoresist layer must also have a thickness sufficient to resist etching. Hence, miniaturization of device can hardly be achieved by reducing thickness of the photoresist layer directly.
Therefore, there is a need in this technical field to provide an improved method for forming patterns, which is capable of minimizing the limitations in photolithographic and etching processes without increasing the complexity of the fabrication process.